In public telecommunication, increased corresponding terminals and enlarged communication traffic volumes are recently causing a squeeze on wireless connection, leading to damages to user's convenience, such as decreased communication rates and interruption of communication. Especially in urban areas where corresponding terminals are densely used, connection is concentrated in a specific base station and therefore exceeds the communication capacity of a wireless portion of the base station, thereby failing to connect even to networks.
In connection between the base station and the terminals, a technology called multiple access is generally used, enabling a plurality of terminals to be apparently connected to one base station at the same time. Examples of a typical technology thereof may include FDMA, TDMA, and CDMA.
FDMA is an abbreviation for “Frequency Division Multiple Access”, and enables connection with a plurality of terminals by allocating a different frequency to each terminal. TDMA is an abbreviation for “Time Division Multiple Access”, and enables connection with a plurality of terminals by dividing a connection time into short time units and allocating this unit time to each terminal. CDMA is an abbreviation for “Code Division Multiple Access”, and enables connection with a plurality of terminals by allocating a specific code to each terminal.
In each of these technologies, the number of terminals that can be connected at the same time has an upper limit. That is, in FDMA, the number of usable frequencies is limited, and therefore the number of terminals that can be connected at the same time has an upper limit. In TDMA, an interval between times to be allocated becomes longer as the number of terminals increases, causing decrease in communication rates. For this reason, the number of terminals that can be connected at the same time has an upper limit in order to maintain a certain quality (which differs depending on, for example, a telephone conversation or a video replay). In CDMA, a code to be allocated needs to have a specific rule (orthogonal code). The number of combinations of such codes has an upper limit, and therefore the number of terminals that can be connected at the same time has an upper limit.
Even with the technologies as described above, there is caused a situation where user's convenience is damaged by the limitation of multiple access due to the increased number of terminals and the concentration of terminals in recent years. Furthermore, communication of control information for allocating frequencies, unit times and codes to a plurality of terminals increases as the number of terminals increases. Accordingly, communication of control information itself also causes a squeeze on communication capacities.
Other than a wireless system involving connection to public networks, a wireless system (for example, a wireless LAN) which enables direct communication in a neighborhood is adopted in recent terminals (direct communication among terminals by this wireless system is referred to as “direct communication”). For example, Patent Literature 1 discloses a method of switching from communication via public networks to direct communication.